In a communication system operating in accordance with the IP (Internet Protocol), data is sent in the form of a data message made up of data packets from a sending node or terminal to a receiving node or terminal. The data message is routed through the system using IP addressing protocols. Some systems also operate in accordance with the Mobile IP Standard defined by the IETF (Internet Engineering Task Force) which is a body that defines internet operating standards and is supervised by the Internet Society's Internet Architecture Board. The Mobile IP Standard as referred to herein is the industry standard of the IETF by which mobile nodes are provided with internet services when they are outside their home network. In particular, the Mobile IP Standard is defined in the documents issued by the IETF as RFC (Request Comments) 3344 dated August 2002 and RFC 3775 dated June 2004. These documents can be seen at http://www.ietf.org/rfc/rfc3344.txt and http://www.irtf.org/rfc/rfc2775.txt.
Each mobile node is identified by a home address and is served by a Home Agent operating in its home network. When attached for service to a network which is not its home network, a mobile node receives a Care Of Address which provides information about the current location at which the mobile node can be reached on the internet.
A mobile node is attached (operably coupled) for communication service to a service node. This attachment is known in the art as a ‘Layer 2’ attachment. ‘Layer 2’ refers to Layer 2 of the OSI (Open Systems Interconnection) well known protocol stack as adopted by the ISO (International Standards Organisation) and is used in the telecommunications industry to indicate functions relating to the data link between two points. The mobile node may switch its attachment from one service node to another. This switching is known in the art as handover or handoff. Where the mobile node remains attached, after handover, to the same network the handover is known more particularly as a ‘Layer 2’ handover. Where the switching of attachment also involves movement from one network to another, the handover is known as ‘Layer 3’ (network-to-network) handover. ‘Layer 3’ refers to Layer 3 of the OSI protocol stack as adopted by the ISO and is used in the telecommunications industry to indicate functions relating to the network level connection between two points.
Where a mobile node which is outside its home network undergoes handover, particularly Level 3 handover, it obtains a new Care of Address associated with the network of the service node to which it becomes attached. The mobile node registers the new Care of Address with its Home Agent so that the Home Agent can forward data messages to the mobile node at the new Care Of Address. The Layer 3 handover is not completed until the new Care Of Address has been notified to and acknowledged by the Home Agent. In the prior art, there can be a considerable delay between the start and completion of a Layer 3 handover. When a mobile node detaches from a network in the handover procedure until it receives a new Care Of Address, the mobile node cannot send or receive IP addressed data messages. Furthermore, between receiving a new Care Of Address and completing the Layer 3 handover procedure, the mobile node can send but cannot receive IP addressed data messages. The period between a mobile node detaching from a network and completing a Layer 3 handover is known in the art as a ‘service break’. Undesirably, significant delay or loss of data messages may take place during a service break using prior art handover procedures.